Device for retrospectively drawing cables into cable protection pipes

ABSTRACT

A device for retrospectively drawing cables into cable protection pipes which are already provided with at least one cable. The device includes an elongated partition floor inserted into the protection pipes. The partition has a central region having an upper and a lower surface. On both sides of the partition, transverse to the central region, there is provided a hollow tubular longitudinal edge which determines the level of the partition floor in the protection pipes. The central region is provided at at least one of the upper and lower surfaces with at least one reinforcing rib extending in the longitudinal direction of the partition floor.

BACKGROUND OF THE INVENTION

The present invention relates to a device for retrospectively drawingcables into cable protection pipes, which are already provided with atleast one cable, including a partition floor which may be inserted intothe protection pipe and which is provided on both sides of its centralregion with a hollow tubular longitudinal edge which determines itslevel.

In one such device which is disclosed in German Patent Specification No.34 27 788 the central region of the partition floor is flat on bothsurfaces thereof, and therefore has a uniform thickness along itscross-section. In practice during insertion it has been shown thatbecause of the increasing friction between the forward region of thepartition floor which is within the cable protection pipe, and theinternal walls of the cable protection pipe or the previously laidcable, that region of the partition floor which is subsequently insertedbuckles under the increasing pressure towards the forward end of thecable protection pipe, and after a further increase in pressure thebuckle collapses towards the front of the partition floor, then afurther buckle forms, which then collapses again, etc. This bucklinginsertion, which is attributable to the insufficient rigidity of thepartition floor for this purpose, has the disadvantage however, thatfirstly insertion cannot be carried out continuously and that secondlythe friction between the partition floor and the cable protection pipeor the cable contained therein is further increased. It would thereforeappear to be worthwhile to further reduce the friction between thepartition floor and the inner wall of the cable protection pipe as wellas between the partition floor and the cable lying therein.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a device forretrospectively drawing a cable into a cable protection pipe of the typementioned above, in which, as a result of reduced friction between thepartition floor and the cable protection pipe internal wall or the cablealready provided in the cable protection pipe, the partition floor canbe inserted in longer strokes in a simpler and more continuous manner.

This object is achieved in a device for retrospectively drawing cablesinto a cable protection pipe of the type mentioned above, in that thecentral region of the partition floor is provided at its upper and/orlower surfaces with at least one reinforcing rib extending in thelongitudinal direction of the partition floor.

The provision of reinforcing ribs increases the longitudinal rigidity ofthe partition floor such that the aforementioned buckling engagement ofthe partition floor when the friction between the partition floor andthe cable protection pipe or the cable contained therein is too high, isavoided, and also the consequent additional friction because of theadditional contact area between the partition floor and the cableprotection pipe is avoided. Furthermore, the contact area between thepartition floor and any cable which is lying in a somewhat undulatingmanner in the cable protection pipe is thus reduced to a minimum, sothat in this way also the friction which must be overcome duringinsertion is reduced to a minimum. Also, the greasing effected to reducefriction between the partition floor and the previously laid cable canbe restricted to narrow areas. In this regard, advantages are alsopresented in the case of pulling through an additional cable over thepartition floor after the latter has been inserted.

When the reinforcing ribs on the upper surface and those on the lowersurface of the central region of the partition floor are arranged inpairs lying directly opposite one another, an arrangement results whichis symmetric about a central plane, which has the advantage that thepartition floor can be inserted in any orientation.

When a pair of reinforcing ribs are arranged centrally in the centralregion of the partition floor the two hollow tubular longitudinal edgeslie relatively close to one another, the cable already in the cableprotection pipe, if of relatively large diameter, cannot jam between thehollow tubular longitudinal edges, and in this way there is avoided apossible increase in friction. The same applies to the cable to besubsequently pulled along the partition floor.

In many instances it is advantageous in a device of the type mentionedto provide two parallel pairs of reinforcing ribs arranged on thecentral region of the partition floor with a gap between them greaterthan the gap between each of them and the corresponding hollow tubularshaped tube edges, that is to say, in particular when the central regionis relatively wide.

For cables of relatively small diameter which have already been laid inthe cable protection pipe and/or cables which are to be pulled throughand which are of relatively small diameter, it may be advantageous toprovide a large number of pairs of reinforcing ribs distributed evenlyover the width of the central region of the partition floor. This isadvantageous even in the case of a very wide central region.

The height of the reinforcing ribs may be at least about the same as thethickness of the central region, but more advantageously, the height maybe about 2 to 3 mm, when the central region has a thickness of about 1.5mm. The cross sectional shape of the reinforcing ribs may be selected tobe approximately semi-circular in cross section. It is also possible,however, to provide reinforcing ribs which are bevelled and which aretriangular in cross section.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the invention may be learned from the descriptionwhich follows in which the invention is described and explained in moredetail with reference to the embodiments illustrated, which is thedrawings. These show:

FIG. 1 in a partially cut away side view, a device for retrospectivelylaying cables in a cable protection pipe according to a first embodimentof the present invention,

FIG. 2 which is a plan view of the device according to the invention,along arrow II of FIG. 1, and shown partially cut away,

FIG. 3, which is a section on line III--III of FIG. 1,

FIG. 4, which is a section similar to that of FIG. 3, but of a secondembodiment of the present invention and

FIG. 5, which is a section similar to that of FIG. 3, but of a thirdembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device 11 according to the invention serves for the preparation forretrospectively drawing into, and also for the retrospective drawinginto or laying of one or more further electrical and/or optical cables15, 13, in a cable protection pipe 14 made of plastic material, or ofearthenware pipes or of other material, which is laid in the ground andalready contains an electrical cable 16, which lies on the floor of theprotection pipe 14. The protection pipe 14 which is generally assembledfrom a number of sections, runs between two access stations, isgenerally used in the laying of, for example, telephone cables but alsoenergy cables, and in terms of its diameter is substantially greaterthan the cable 16 itself, so that there still remains sufficient spaceinside the protection pipe 14 for the laying or drawing in of furthercables. For this purpose the device 11 uses a partition floor 12, whichmay be drawn into the previously laid cable protection pipe 14 byinsertion, and on which the one or more further cables 15 may be laid.The partition floor 12 has on both sides of the central region 17, thatis on both of its long side edges, tubes 18 and 19 respectively, whichhave a hollow circular cross sectional cavity 21 extending along theirentire length, into each of which at least one further and preferablyoptical cable 13 can be drawn.

The partition floor 12, which serves to spatially separate and also, insome cases, to electrically separate the previously laid cable 16 on theone hand and the retrospectively laid cable 15, 13 on the other hand, ismade for example from a transversely stiff plastic material, such aspolyamide, polyester or hard P.V.C.

The partition floor 12 is integrally formed, for example extruded, andcomprises, as mentioned above, a strip shaped central region 17, to thetwo longitudinal edges of which the tubes 18, 19 are connected, whichhave a circular cross sectional cavity 21 extending along their fulllength. In spite of the transverse rigidity of the partition floor 12,this is preferably longitudinally flexible, so that it may be coiled,that is to say may be taken up on a drum so that it may be cut offaccordingly after completion of insertion in the cable protection pipe14.

The strip-shaped central region 17 comprises, according to FIG. 3, onits upper side 56 as well as on its lower side 57, along its entirelength, two mutually parallel reinforcing ribs 58, 59 and 60, 61respectively. The distance between the parallel reinforcing ribs 58, 60and 59, 61 is greater than each of their respective distances from thecorresponding tubes 18 and 19 respectively. The reinforcing ribs 58 and60 and 59 and 61 are each arranged directly opposite one another and areintegrally formed, or extruded, with the central region 17 or the entirepartition floor 12. The reinforcing ribs 58 to 61 as shown in theillustrated embodiment have a semi-circular cross section, but it shouldbe understood that they may have other shapes, for example triangular incross section and with a flattened apex. The thickness of thereinforcing ribs 58 to 61 is in the interval between the single and thedouble thickness of the central region 17.

FIG. 4 shows, in accordance with another embodiment of the presentinvention, that the central region 17' of the partition floor 12' isprovided on its upper side 56' and on its lower side 57' with a singlecentrally located reinforcing rib 62' and 63' respectively. This isadvantageous where, because the central region 17' is relatively narrow,the two tubes 18 and 19 lie closer together than in the embodiment ofFIG. 3.

FIG. 5 shows an embodiment comprising a partition floor 12", the centralregion 17" of which is relatively wide and which is provided with alarge number of reinforcing ribs 64 and 65, which lie in pairs oppositeone another and follow one another in sequence at short sidewaysintervals.

As is shown in the drawings, the full width of the partition floor 12,12' or 12" respectively is at most equal to but is generally less thanthe internal diameter of the already laid cable protection pipe 14, sothat the hollow tubular longitudinal edges 18, 19 also determine theclearance of the partition floor 12, 12' or 12" during insertion in theprotection pipe 14. This also allows the height of the partition floor12, 12', 12" to change within the cable protection pipe 14, depending onwhere the previously laid cable 16 lies. In FIGS. 3 to 5 the partitionfloor 12, 12', 12" lies with its longitudinal edges 18, 19 on theinternal wall of the cable protection pipe 14 above or below thelongitudinal central plane and/or the cable 16 which was already laid inthe cable protection pipe 14.

The internal diameter of the hollow tubes, or hollow tubular shapedlongitudinal edges 18, 19, which are advantageously of the samediameter, is large enough to receive at least one further cable, forexample in the form of a relatively thin optical cable 13. An optical orglass fiber cable 13 of this type, can be either laid in the partitionfloor 12, 12' or 12" which is to be inserted, or can be subsequentlypulled through by means of a previously laid towing line.

The device 11 according to the invention consists of, in addition to thepartition floor 12, 12', 12", the clearance of which is determined bythe tubes 18, 19, a cable guide 25 which serves such that when duringinsertion of the partition floor 12 the latter and the previously laidcable 16 come towards one another, then, either the cable 16 is pusheddownwardly or the partition floor 12 yields obliquely and/or is pushedupwardly and in this way the previously laid cable 16 is not damaged.The cable guide 25 which is preferably of plastic material consists inthis case of three parts, namely head elements 26, 27 for insertion ineach hollow tube 18, 19 and a guide element 28 which may be fitted overthe central region 17 of the partition floor 12. The two head elements26 and 27, which are closed at one end and are hollow, and are of thesame construction as one another, each comprises two regions, namely arear externally cylindrical region 31 and an integrally formedexternally conical region 32 connectable thereto, the smallest diameterof which constitutes the forward closed and rounded end 33. The externaldiameter of the cylindrical region 31 corresponds to the internaldiameter of the tubes 18, 19, so that it can be inserted in these. Theforward conical region 32 is connected by means of an annular shoulder38 to the rear region 31. The width of the annular shoulder 38corresponds to the wall thickness of the tubes 18, 19.

The guide element 28, which is likewise of plastic material, is in theshape of a reclining U, and therefore is rounded at its forward free end46 and has a width corresponding to that of the central region 17 of thepartition floor 12. The gap 49 between the two limbs 47 and 48 of the Uhas a clearance which is the same as or is somewhat less than thethickness of the central region 17 including the reinforcing ribs 58 to65. It is also possible to provide a gap 49 having a clearancecorresponding basically to the thickness of the central region 17without ribbing, and to provide in the two limbs 48 and 49 grooves forreceiving the engaging reinforcing ribs 58 to 65. In this way thecentral region 17 of the partition floor 12 can be received as africtional fit in the gap 49. In the construction shown in FIG. 1 theupper limb 47 is made thicker than the lower limb 48 and is provided atthat end 51 which is further from the insertion end of the partitionfloor 12, with a threaded bore 52 into which a corresponding threadedelement may be screwed in a manner which is not shown, which may forexample be connected to a towing line or the like, so that this towingline may be pulled into the cable protection pipe 14 simultaneously withthe partition floor 12.

The retrospective insertion of the partition floor in a cable protectionpipe 14 laid in the ground, in which a cable 16 is already laid, iseffected by inserting the partition floor 12, 12' or 12" provided at itsfront end with a cable guide 25, with the help of a drive device or withshort strokes of the hand, the cable guide 25 sliding along the internalwall 24 of the cable protection pipe and over the already laid cable 16,and possibly pushing the latter to one side or another in the directionof the protection pipe floor or itself yielding in an oblique manner.The partition floor 12, 12', 12" moves correspondingly into theprotection pipe 14, that is it slides along the protection pipe internalwall 24 and disposes itself corresponding to the disposition of thecable guide 25. It does not matter here whether the cable guide 25, orthe partition floor 12, is exactly horizontal as shown in the drawingsor extends obliquely in one direction or the other, that is to say isdisposed in an inclined manner within the protection pipe 14, as in thiscontext the term "partition floor" includes also the term "partitionwall" when in an extreme case the cable guide 25 and/or the partitionfloor 12 is inclined or is upright. Because the partition floor 12 isflexible, the disposition is determined by the disposition of thepreviously laid cable 16 in the protection pipe 14. Due to thearrangement of the reinforcing ribs 58 to 65 a certain definite rigidityis furthermore given in the longitudinal direction, so that even whenthe friction is relatively large, the partition floor 12, 12', 12" doesnot stop in the cable protection pipe 14.

I claim:
 1. A device for retrospectively drawing cables into cableprotection pipes which are already provided with at least one cable,including:an elongated partition floor inserted into the protectionpipes, which has a central region having an upper and lower surface, andis provided on both sides transverse to the central region with a hollowtubular longitudinal edge which determines its level in the protectionpipes, wherein the central region is provided with a reinforcing rib oneach surface of the central region extending in the longitudinaldirection of the partition floor, and wherein both reinforcing ribs arelocated at the center of the central region.
 2. A device forretrospectively drawing cables into cable protection pipes which arealready provided with at least one cable, including:an elongatedpartition floor inserted into the protection pipes, which has a centralregion having an upper and lower surface, and is provided on both sidestransverse to the central region with a hollow tubular longitudinal edgewhich determines its level in the protection pipes, wherein at least onepair of reinforcing ribs are provided on each surface of the centralregion extending in the longitudinal direction of the partition floor,said pairs of reinforcing ribs being directly opposite to one another,and wherein the gap between the reinforcing ribs of each pair is greaterthan the gap between each reinforcing rib and its corresponding hollowtubular longitudinal edge.
 3. The device as defined in claim 2, whereineach reinforcing rib has a height which is at least equal to thethickness of the central region.
 4. The device as defined in claim 2,wherein each reinforcing rib is approximately semi-circular in crosssection.
 5. The device as defined in claim 1, wherein each reinforcingrib has a height which is at least equal to the thickness of the centralregion.
 6. The device as defined in claim 1, wherein each reinforcingrib is approximately semi-circular in cross section.